Low inertia tremolo unit

ABSTRACT

A rotating tremolo unit of the type consisting of a rotating drum having a speaker cone mounted in the periphery thereof characterized by a displacement of the driver element of the cone to or beyond the center of rotation of the system to balance the rotating mass, and low peripheral mass.

United States Patent Schrecongost Sept. 16, 1975 [54] LOW INERTIA TREMOLO UNIT 2,881,850 4/1959 Bonn 181/153 2.900.453 1959 k 181 [75] lnvemo Ray Schremngmt, Park Ridge 3,192,322 3/1965 1811. 11 3 3,347,337 10/1967 Mochida eta]... 181/31 B [73] Assignee: Hammond Corporation, Chicago 3,517,769 6/1970 Broussard 181/31 B 111. I Primary Examiner-Stephen J. Tomsky [22] Ffled' 1973 Attorney, Agent, or Firm-Lowell C. Bergstedt [21] App]. Nos. 410,512

[57] ABSTRACT 521 [1.8. c1 131/143; 181/153 A rotating tremolo unit of the type consisting of a 51 11 1. Cl. G10K 7/00; HOSK 5/00 wing drum having a Speaker cone mounted in the 1581 new of Search 181/27 A1 1991 riphery thereof characterized by a displacement of the 181/151 153; 84/124 1'25; 179/1 J driver element of the cone to or beyond the center of rotation of the system to balance the rotating mass, [56] References Cted and low peripheral mass.

UNITED STATES PATENTS Telkowski 181/27 A 7 Claims, 4 Drawing Figures LOW INERTIA TREMOLO UNIT BACKGROUND OF THE INVENTION Rotating tremolo units have characteristically been drum-shaped speaker enclosures adapted for rotation on their cylindrical axis with a conventional speaker mounted inthe periphery of the drum. counterbalancing means are commonly situated within the drum opposite thespeaker to balance the assembly and avoid vibration, noise, and bearing wear. The speaker employed is conventional with a cone directly connected to a driver unit consisting of a permanent magnet and voice coil assembly which is relatively heavy and substantially displaced from the axis of rotation of the drum. The counter-balance, in practice, substantially doubles the moment of inertia of the overall assembly. In addition, the drum-shaped enclosure has typically been constructed of masonite which also contributes substantially to the inertia of the unit.

A performer at an electronic organ or the like expects a response to tonal quality controls relatively immediately. If a performer cues a tremolo tone, he does not want to wait appreciable seconds for the tremolo to develop or stop. A unit with a high moment of inertia will require either such time to accelerate or decelerate or a motor of a size grossly disproportionate to the normal operating needs of the system.

SUMMARY OF THE INVENTION This invention contemplates the separation, in a speaker system, of the. driver assembly from the speaker cone and its location at the approximate center of rotation of the tremolo unit such that only the speaker cone, which has negligible mass in comparison with the driver, has any appreciable moment arm. The driver unit is connected to the speaker cone by a longitudinally rigid connecting element which serves to drive the cone as effectively as if it were directly connected to the driver unit. It is further contemplated that the center of mass of the driver unit be displaced from the center of rotation of the drum oppositely to the cone to counterbalance the mass of the cone and its supporting structure and thereby avoid the requirement of a separate counterbalancing element. It is further contemplated that the rigid and strong element necessary to support the drum for rotation and to support the driver unit and cone be reduced to a diametrical strut, and the balance of the drum be defined by a pair of lightweight shells formed of polystyrene foam or the like to further reduce the peripheral rotating mass of the drum unit and thereby make acceleration or deceleration of the unit quickly possible with reasonable motor power.

a, r BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a tremolo unit embodying this invention;

FIG. 2 is a" partial side elevation of the'strut of FIG. 1 with the attached cone and driver in section,

FIG. 3 is aview similar to FIG. 1 illustrating-an optional form of 'the invention; and

FIG. 4 is a section through the center block of FIG. 3 looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT The tremolo unit 10 of the present invention comprises a diametrical strut l2 and a pair of lightweight, foam, semi-cylindrical shells 14. The strut 12 is a plastic or wooden rectangular member mounting a pair of shafts or stub axles l6 and 18 centrally on its long edges and blanked out to the front and rear of its axis of rotation to define front and rear ribs 20 and 22, a central rib 24 and longitudinal edges 26 and 28. The thickness of the strut 12 is sufficient to accommodate the shafts 16 and 18 in appropriate bores in which they are secured.

The front edge 30 of the central rib 24 has a central rectangular notch 32 formed therein to receive a speaker driver assembly 34. The driver is a conventional fourinch speaker having a basket 36 with a pcripheral flange 38 perforated for mounting screws 40 extending into the front edge 30 of the center strut on either side of the notch 32 and a permanent magnet 42 mounted to the rear of the basket 36 and contained in the notch 32. A voice coil 44 is supported by a spider 46 and the speaker cone 48 so as to be concentric with the permanent magnet pole piece 50. The voice coil form 52 extends through the apex of the cone 48 and is closed by a dome 54. The voice coil leads 56 are connected to eyelets 57 in the cone which in turn are connected electrically by leads 59 extending through the basket 36 to the axles l6 and 18, the leads 59 being secured under the heads of screws 58 extending through the face of rib 24 into electrical contact with the shafts- 16 and 18. The shafts have spring metal contacts 60 bearing against their ends at their center of rotation connected appropriately to an amplifier.

A pair of notches are formed in the longitudinal edges 26 and 28 at their intersection with the front rib 20 to define front facing surfaces 62 in the long edges to which opposite sides of a six X nine-inch speaker frame 64 are secured as by screws 65. The front rib 20 has bores 67 therein aligned with the screws 65 through which the screws are tightened down on the speaker frame. The speaker frame has a six X nine-inch speaker cone 66 cemented thereto characterized, however, by the absence of a direct driver or any normally associated parts. Instead, the apex of the speaker cone has a center aperture 68 which would otherwise be occupied by the voice coil form and dome.

A stiff paper cylinder 70 proportioned to fit closely within the aperture 68 and slightly longer than the normal expected spacing between the aperture 68 and the dome 54 is cemented at its end 72 to the dome and externally as at 74 to the edge of the aperture 68 of cone 66, so linking cone 66 rigidly yet lightly to the voice coil from 54. Thus, as the voice coil vibrates, the motion is transmitted by the cylinder to the six X nine-inch cone 66, and the mass of the linkage is sufficiently slight such that the transmission is essentially without distortion.

The excess length of the cylinder, of course, is to accommodate certainly to manufacturing and assembly variations in the spacing between the dome 54 and the apex of cone 66. The driver 34 and the speaker frame 64 are mounted respectively in their ultimate locations on the strut, and the cylinder 70 is then cemented to the cone 66 and dome 54 as at 72 and 84, so resulting in an unstressed driving connection, free from distortion.

Other methods have been conceived of making the connection between the driver and the cone. Shorter, telescoping cylinders may be connected, each, to the cone and the driver and cement applied to the final assembly on the circumference of the overlap of the telescoped cylinders. A light rigid wire may be soldered to eyelets respectively in the dome and cone. A composite structure of a double tapering paper cylinder with short lengths of wire at its ends for dome and cone connection has been considered. The advantage of the principal described form is that it seems simplest and least expensive.

The driver, as described in a four-inch speaker. A special driving unit lacking the cone 48 and related structure could undoubtedly be employed, but such a special product would probably be more expensive than a common four-inch speaker. The fact that the driver speaker is a sound producer also does not impair the operation of the device. First, the audio output supplied to both cones is the same. Second, the output of the six nine-inch cone will swamp that of the fourinch cone because of the area difference and because the four-inch cone is wholly housed within a soundabsorptive chamber and has no baffle.

The tremolo unit is completed by a pair of styrofoam bead or equivalent foamed plastic shells 14. They, with the strut 12, define a drum or cylinder, and thus each is a slightly less than semicircular drum half consisting of approximately semicircular end walls 76 and a corresponding arcuate side wall 78. The side walls are concavely recessed as at 80 to conform to the six nineinch speaker frame 64 and expose the cone 66. The thickness of the shells is such that the cutouts or recesses 80 fit the frame 64, and the assembly thus provides an effective baffle for the speaker 66. The strut 12 has locating pins 82 extending laterally out from the corners thereof and the shells have corresponding recesses 84 therein to assure a proper alignment of the parts. The shells desirably are cemented to the faces of the strut or banded to complete the assembly.

From the foregoing description it will be appreciated that the above invention meets excellently and in novel fashion the desired objection of a low moment tremolo assembly. It provides a baffled speaker wherein the primary massive element is situated on the axis of rotation. The mass of peripheral elements has been reduced to a minimum. This derives from the displacement of the speaker driver from direct association with the speaker cone to the center of the system and from the concept of mounting the speaker elements on a relatively thin diametrical strut. This being the primary supportive structure, the remainder of the enclosure can be constituted by the foamed half-cylindrical shells.

A further refinement of this invention resides in the possibility of avoidance of counterbalancing so further reducing the rotational moment. Once the concept of separating the driver from the cone is arrived at, it becomes possible to use the massive driver element as the counterbalance itself by positioning its center of mass minor distances from the axis of rotation to compensate any imbalance in the system. Dependent on the exactness of counterbalance desired, the front edge 30 of the center strut 24 can be positioned to achieve this balance, determined by the allowable tolerances of the driver, the speaker, and the strut 24. Alternatively for greater precision, the driver could be adjustable with respect to the axis of rotation of the unit (on the front edge 30) in obvious fashion to obtain a more precise balance.

FIGS. 3 and 4 illustrate an optional configuration of the invention. In this modification, a vertically oriented flat block 100, here shown to be octagonal, is hollowed out from the back side into a sort of centrally apertured dish with a peripheral flange 102 and an annular front lip 104 surrounding a central aperture 106. The driver unit 108, which may be identical with the driver 34 of the first described form, is secured by screws 1 10 to the w front side of the lip 104 with the permanent magnet 112 of the driver extending through the aperture 106 into the hollowed out back of the block 100. Stub axles 114 are secured oppositely in the flange 102 of the block to mount the assembly for rotation as the stub axles 16 of the principal described form. Electrical connection of the voice coil leads 116 of the driver unit 108 are made in any suitable form to the stub axles 1 14.

The strut, in this modification, consists of a horizontal frame 120 constructed on the block with the block occupying generally a central position. The frame consists of side rails 122 contained in central notches 124 in the vertical edges of the block 100, a rear end piece 126 spanning the side rails at'the rear end and a front end piece 128 spanning the side rails at the front end. The side rails 122 arenotched out adjacent the front end piece 128 to provide a shoulder comparable to the shoulder 62 of the principal described form to which the mounting flange 130 of a speaker cone 132 may be secured in the same fashion as illustrated in FIG. 2. The front end piece 128 is provided with holes 134 for the insertion of screws into the speaker cone flange 130 connecting it to the side rails 122.

The speaker cone 132 is desirably connected to the driver assembly 108 by a cylindrical paper tube 136 precisely as described in the principal modification hereof. It will be evident, of course, that the other sorts of linkages described above between the cone and the driver can be employed in this case as well as in that.

The horizontal frame 120 has locating pins 138 extending upwardly and downwardly from the corners thereof for purposes of locating accurately the baffle shell 140.

The baffle 140 in this modification is again a foamed plastic cylindrical or drum-shaped enclosure formed desirably of expanded polystyrene bead material divided into two identical shells. In this case, however, the plane of division of the baffle into the two shells is perpendicular to the axis of the drum rather than containing the axis. Thus, the shell halves 142 are shallow, cylindrically walled cups. The walls have semi-elliptical cutouts 144 formed therein to conform to and expose the speaker cone 132 for sound emission. On either side of the cutout, depressed shoulders 146 are provided with vertical holes in the horizontal surfaces to accommodate the ends of the front end piece 128 and of the associated locating pins. Opposite the semielliptical cutout, the cylindrical edge of the shell is notched to receive half the thickness of the rear end piece 126 and has holes therein to receive the associated locating pins. The shell halves are centrally perforated as at 152 to receive the stub shafts 114 which are long enough to extend through the material of the shell halves and be received in bearings and arranged for electrical connection as shown in FIG. 2 hereof.

The shell halves 142 will, of course. be secured to the end segments 128, 126 and to each other along the free edges thereof as by an adhesive, etc. So assembled, the unit provides the full functional equivalent of the structure described in FIGS. 1 and 2, although the structural conception is somewhat different. It will be appreciated that here, as in the modification of FIG. 1, the shell halves are identical and a single mold may thus provide both halves of the enclosure.

I claim:

1. A tremolo assembly for an electronic musical instrument comprising:

an enclosure of sound absorbing material defining a central axis and a sound-transmitting opening in a peripheral area thereof spaced from said central axis;

means for supporting said enclosure for rotation about said central axis;

a speaker cone mounted in said peripheral area of said enclosure adjacent said sound-transmitting opening;

a driver assembly for said speaker cone, including a voice coil form, mounted within said enclosure at a position such that said central axis of said enclo sure intersects said driver assembly; and

a longitudinally rigid coupling element mounted between said voice coil and said speaker cone;

whereby the moment of inertia of said tremolo assembly is substantially reduced to permit rapid acceleration and deceleration thereof.

2. Apparatus as claimed in claim 1, wherein said means for supporting said enclosure comprises a support structure mounted internally of said enclosure and intersecting said central axis thereof; said support structure having a front rib for mounting said speaker cone adjacent said sound transmitting opening, a central rib for mounting said driver asembly, and an opening communicating between said front and central ribs for receiving said coupling element.

3. Apparatus as claimed in claim 2, wherein said enclosure comprises a pair of shells having complementary shapes mounted on opposite sides of said support structure, said shells being formed of lightweight, foamed plastic to minimize the moment of inertia of said tremolo assembly.

4. Apparatus as claimed in claim 1, wherein said coupling element comprises a cylindrical tube fastened at one end to said voice coil form and at the other end to the apex of said speaker cone.

5. Apparatus as claimed in claim 1, wherein said driver assembly comprises a high compliance, small diameter speaker.

6. A tremolo assembly for an electric musical instrument comprising:

an enclosure;

a speaker cone; and

a driver assembly for said speaker cone;

said enclosure comprising a transverse strut and a pair of shells secured to opposite sides of said strut, said strut being adapted to rotate said enclosure about a central axis and to mount said speaker cone and said driver assembly internal to said enclosure with at least said speaker cone mounted adjacent a peripheral area of said enclosure, said pair of shells having complimentary shapes to define a sound-transmitting opening in said enclosure adjacent said speaker cone and being constructed of lightweight foamed plastic to reduce the moment of inertia of said tremolo assembly.

7. Apparatus as claimed in claim 6, wherein said strut is adapted to mount said driver assembly with its center of mass substantially at said central axis to minimize the moment of inertia of said tremolo assembly and thereby to permit rapid acceleration and deceleration thereof, and a coupling element is mounted between said driver asembly and said cone. =l 

1. A tremolo assembly for an electronic musical instrument comprising: an enclosure of sound absorbing material defining a central axis and a sound-transmitting opening in a peripheral area thereof spaced from said central axis; means for supporting said enclosure for rotation about said central axis; a speaker cone mounted in said peripheral area of said enclosure adjacent said sound-transmitting opening; a driver assembly for said speaker cone, including a voice coil form, mounted within said enclosure at a position such that said central axis of said enclosure intersects said driver assembly; and a longitudinally rigid coupling element mounted between said voice coil and said speaker cone; whereby the moment of inertia of said tremolo assembly is substantially reduced to permit rapid acceleration and deceleration thereof.
 2. Apparatus as claimed in claim 1, wherein said means for supporting said enclosure comprises a support structure mounted internally of said enclosure and intersecting said central axis thereof; said support structure having a front rib for mounting said speaker cone adjacent said sound transmittIng opening, a central rib for mounting said driver asembly, and an opening communicating between said front and central ribs for receiving said coupling element.
 3. Apparatus as claimed in claim 2, wherein said enclosure comprises a pair of shells having complementary shapes mounted on opposite sides of said support structure, said shells being formed of lightweight, foamed plastic to minimize the moment of inertia of said tremolo assembly.
 4. Apparatus as claimed in claim 1, wherein said coupling element comprises a cylindrical tube fastened at one end to said voice coil form and at the other end to the apex of said speaker cone.
 5. Apparatus as claimed in claim 1, wherein said driver assembly comprises a high compliance, small diameter speaker.
 6. A tremolo assembly for an electric musical instrument comprising: an enclosure; a speaker cone; and a driver assembly for said speaker cone; said enclosure comprising a transverse strut and a pair of shells secured to opposite sides of said strut, said strut being adapted to rotate said enclosure about a central axis and to mount said speaker cone and said driver assembly internal to said enclosure with at least said speaker cone mounted adjacent a peripheral area of said enclosure, said pair of shells having complimentary shapes to define a sound-transmitting opening in said enclosure adjacent said speaker cone and being constructed of lightweight foamed plastic to reduce the moment of inertia of said tremolo assembly.
 7. Apparatus as claimed in claim 6, wherein said strut is adapted to mount said driver assembly with its center of mass substantially at said central axis to minimize the moment of inertia of said tremolo assembly and thereby to permit rapid acceleration and deceleration thereof, and a coupling element is mounted between said driver asembly and said cone. 